1. Field of the Invention
The present invention relates generally to a rotary dial unit, and is directed more particularly to a rotary dial unit which is simple-structured, inexpensive and capable of retaining its adjusted position even if the knob thereof is vibrated or inadvertently touched, and hence is suitable for use with precision control instruments or the like.
2. Description of the Prior Art
In a variable resistor for precision control instruments, it is necessary that the slider thereof be held accurately at its adjusted position on the resistance element thereof, but in a prior art variable resistor the slider thereof may sometimes get out of the adjusted position due to vibrations applied to the variable resistor or an accidental touch thereto by the operator.
To avoid this, conventional variable resistors of this kind are provided with various clamp means. The clamp means employed in the past has, for example, such an arrangement that a brake lever for clamping use is turned to urge a brake shoe against the inner marginal edge of a knob of the variable resistor, or the peripheral surface of a cylindrical member rotatable with the rotary shaft of the knob concentrically therewith is pressed in the direction perpendicular to the lengthwise direction of the rotary shaft, or an annular surface of the base portion of the knob which is perpendicular to the lengthwise direction of the rotary shaft is pressed in the vertical direction, thereby preventing an unnecessary rotational movement of the knob.
In general, however, the abovesaid prior art clamp means are complex in construction, which is an obstacle to the manufacturing of rotary dial units at low cost.